Issue #136 contained a program that demonstrated the way to download files from the internet. After it was released, it was found to fail for some people. Further investigation showed that the function to check the validity of a URL required a unicode (also called "wide") character string. Liberty BASIC uses ASCII strings, so the URL string requires conversion before it is sent to the function. For more on ASCII and unicode, see DEFINITIONS This conversion can be accomplished with the API function from kernel32.dll called MultiByteToWideChar. I've adapted some code provided by Stefan Pendl that uses this function to convert strings.

The function is as follows. If the function succeeds, it returns the unicode string. If it fails, it returns an empty string, and the demo program traps that error. Each argument is commented.

function MultiByteToWideChar$(String$)
    'converts any string into unicode
    CodePage = 0  :  dwFlags = 0
    cchMultiByte = -1
    lpMultiByteStr$ = String$
    cchWideChar = len(String$) * 3
    lpWideCharStr$ = space$(cchWideChar)

    calldll #kernel32, "MultiByteToWideChar", _
    CodePage as ulong, _    'CP_ACP=0, ansi code page
    dwFlags as ulong, _     'use 0, flags for character translation
    lpMultiByteStr$ as ptr,_'the ascii string to convert
    cchMultiByte as long, _ 'len of string, -1 for null-terminated string
    lpWideCharStr$ as ptr, _'buffer for returned ansi string
    cchWideChar as long, _  'size in wide characters of string buffer
    result as long          'returns number of wide characters written to buffer

    if result = 0 then
        MultiByteToWideChar$ = ""
    else
        MultiByteToWideChar$ = left$(lpWideCharStr$, result * 2)
    end if
    end function

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UNICODE AND ASCII

Definition of UNICODE from [WikiPedia.org]

Definition of ASCII from [WikiPedia.org]

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CORRECTED DEMO

'Download html from given
'URL to file on disk.
'
'Minimum availability Internet Explorer 3.0
'Minimum operating systems Windows NT 4.0, Windows 95
'

'check for valid URL for HTML page:
u$ = MultiByteToWideChar$("http://www.libertybasic.com/index.html")

if u$ = "" then
    print "Unable to convert URL to unicode string."
    end
end if

'if result = 0, URL is valid
result = ValidURL(u$)

if result = 0 then
    'download html from libertybasic.com
    downloadresult = DownloadToFile("http://www.libertybasic.com/index.html", DefaultDir$ + "\test.htm")
    if downloadresult <> 0 then print "Error downloading libertybasic.com HTML file."

    open DefaultDir$ + "\test.htm" for input as #f
    test$ = input$(#f, LOF(#f))
    close #f

    print test$ 'print HTML from file into mainwin
    print : print
    print "The text above was downloaded from http://www.libertybasic.com/"
else
    print "Invalid URL:"; u$
end if

'now attempt to download the banner:
result = DownloadToFile("http://www.libertybasic.com/lb3banner.jpg", DefaultDir$ + "\banner.jpg")
if result <> 0 then
    print "Error downloading Liberty BASIC banner."
else
    run "mspaint.exe " + chr$(34) + DefaultDir$ + "\banner.jpg" + chr$(34)
    print : print : print "Done"
end if

wait

Function DownloadToFile(urlfile$, localfile$)
    open "URLmon" for dll as #url
    calldll #url, "URLDownloadToFileA",_
    0 as long,_         'null
    urlfile$ as ptr,_   'url to download
    localfile$ as ptr,_ 'save file name
    0 as long,_         'reserved, must be 0
    0 as long,_         'callback address, can be 0
    DownloadToFile as ulong  '0=success
    close #url
end function

Function ValidURL(urlfile$)
    open "URLmon" for dll as #url
    calldll #url, "IsValidURL",_
    0 as long,_         'ignored, must be 0
    urlfile$ as ptr,_   'urlfile to check
    0 as ulong,_        'ignored, must be 0
    ValidURL as long
    close #url
end function


function MultiByteToWideChar$(String$)
    'converts any string into unicode
    CodePage = 0  :  dwFlags = 0
    cchMultiByte = -1
    lpMultiByteStr$ = String$
    cchWideChar = len(String$) * 3
    lpWideCharStr$ = space$(cchWideChar)

    calldll #kernel32, "MultiByteToWideChar", _
    CodePage as ulong, _    'CP_ACP=0, ansi code page
    dwFlags as ulong, _     'use 0, flags for character translation
    lpMultiByteStr$ as ptr,_'the ascii string to convert
    cchMultiByte as long, _ 'len of string, -1 for null-terminated string
    lpWideCharStr$ as ptr, _'buffer for returned ansi string
    cchWideChar as long, _  'size in wide characters of string buffer
    result as long          'returns number of wide characters written to buffer

    if result = 0 then
        MultiByteToWideChar$ = ""
    else
        MultiByteToWideChar$ = left$(lpWideCharStr$, result * 2)
    end if
    end function

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